(1) Field of the Invention
The present invention relates to an expansion valve, and more particularly, to an expansion valve which is responsive to the temperature of refrigerant delivered to a compressor from an evaporator in a refrigeration cycle to control the quantity of the refrigerant introduced into the evaporator.
(2) Description of the Related Art
In an air conditioning system for automobiles, a refrigeration cycle is constructed in which high-temperature high-pressure gaseous refrigerant compressed by a compressor is condensed in a condenser and the resulting high-pressure liquid refrigerant is adiabatically expanded in an expansion valve to obtain low-temperature low-pressure liquid refrigerant, which is then evaporated in an evaporator and returned to the compressor. The evaporator, to which the low-temperature refrigerant is supplied, exchanges heat with the air in the vehicle compartment, whereby the compartment is air-cooled.
The expansion valve includes a temperature-sensitive chamber of which the internal pressure rises or drops in response to temperature changes of the refrigerant in a low-pressure refrigerant passage connected to the outlet of the evaporator, and a valve mechanism actuated in response to pressure rise or drop of the temperature-sensitive chamber to control the flow rate of the refrigerant supplied to the inlet of the evaporator. The valve mechanism is housed in a valve casing, whose refrigerant inlet and outlet are respectively connected by fastening members, such as nuts, to a high-pressure refrigerant pipe and a low-pressure refrigerant pipe leading to the evaporator. A temperature sensing cylinder is connected to the temperature-sensitive chamber and has a distal end portion thereof closely fixed to a refrigerant pipe connected to the outlet of the evaporator to sense the temperature of the refrigerant at the outlet of the evaporator.
Originally expansion valves are designed to detect not only the temperature but the pressure of the refrigerant at the outlet of the evaporator so that the valve mechanism may be controlled also in response to variations in the pressure. There has, however, been a demand for expansion valves reduced in cost. To meet the demand, an expansion valve has been developed which senses only the temperature of the refrigerant at the outlet of the evaporator, as mentioned above, and in which a joint between the refrigerant pipe connected to the outlet of the evaporator and the refrigerant pipe leading to the compressor is omitted to cut down the cost. This arrangement is based on the fact that, when the refrigerant from the expansion valve passes through the evaporator, its pressure loss within the evaporator is almost constant and thus a pressure obtained by subtracting the pressure loss from the pressure at the outlet of the expansion valve can be regarded as the pressure of the refrigerant at the outlet of the evaporator.
Even in this temperature sensing type expansion valve which requires no connection of refrigerant pipes on the outlet side of the evaporator, it is necessary that the high-pressure refrigerant pipe and the low-pressure refrigerant pipe leading to the evaporator should be connected, respectively, to the refrigerant inlet and outlet of the valve casing by fastening members when the expansion valve is assembled. Accordingly, there has been a demand for expansion valves which are further reduced in cost, inclusive of the assembling cost.
The present invention was created in view of the above circumstances, and an object thereof is to provide an expansion valve which permits both the assembling cost and the cost of parts to be effectively reduced by a large margin and thus is highly economical.
To accomplish the above object, according to the present invention, there is provided an expansion valve for sensing temperature change of a refrigerant at an outlet of an evaporator to control a flow rate of the refrigerant supplied to an inlet of the evaporator. The expansion valve comprises an expansion valve unit including a temperature-sensitive chamber whose internal pressure rises or drops in response to temperature change of the refrigerant in a low-pressure refrigerant pipe connected to the outlet of the evaporator, and a valve mechanism actuated in response to pressure rise or drop of the temperature-sensitive chamber to control the flow rate of the refrigerant supplied to the inlet of the evaporator, a valve casing having an opening into which said expansion valve unit is fitted, said valve casing being formed integrally with a high-pressure refrigerant pipe for introducing the high-pressure refrigerant, a low-pressure refrigerant pipe for letting out the refrigerant whose flow rate has been controlled, and the evaporator and fixing means for fixing said expansion valve unit fitted into said valve casing.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.